A micro-mirror actuator is a microelectromechanical component for dynamically modulating light. For micro-mirror actuators, a distinction is made between so-called microscanners and spatial light modulators.
In microscanners, a light beam is modulated on a continuously moved individual mirror. Light may be guided or “scanned” over a projection surface with grazing incidence. Microscanners are used in projection displays, bar code scanners, in endoscopy, and in spectroscopy, among other areas.
In spatial light modulators, the light is modulated via a mirror matrix. The individual mirrors undergo discrete deflections over time. The deflection of partial beams, i.e., a phase-shifting effect, is thus achieved. With the aid of a matrix configuration, micro-mirror actuators are able to deflect the light of a strong light source in such a way that an image is projected.
The micro-mirror actuators are generally composed of individual elements, configured in a matrix, in which the individual micro-mirror is composed of a tiltable reflective surface having an edge length of a few microns. The motion is brought about by the action of force of electrostatic fields. The angle of each micro-mirror may be individually adjusted, and the micro-mirror generally has two end states between which it is able to alternate up to 5000 times per second.
The mirror should be precisely deflected in order to direct the light beam exactly to a desired location. For example, a light beam composed of pixels should be directed in a targeted manner into one region in order to systematically and homogeneously establish an image.
To detect the deflection of the micro-mirror actuator, position sensors, in particular piezoresistive sensors, are mounted on the micro-mirror element or in close proximity thereto. Such sensors are able to detect vibrations and deflections. If a force is exerted on the mirror for the deflection, this results in a change in voltage at the output of the sensor.
The output voltage of such a sensor ideally has a curve as a function of the micro-mirror deflection which is ascertainable by measurement. The actual curve has several compensatable systematic errors, such as linearity errors and offset errors, as well as random errors due to instrument-related fluctuations.
It is known that a change in temperature for position sensors, in particular piezoresistive sensors, results in a zero shift of the sensor output voltage (change in the offset voltage). The static error characteristic curve and the temperature characteristic may be ascertained for the sensors and corrected via suitable compensation algorithms in the control and evaluation electronics system. The ambient temperature and the change in temperature of the sensor may be ascertained by a temperature sensor. The temperature-dependent zero shift of the sensor output voltage is thus continuously ascertainable, and may be taken into account in the compensation algorithm.